| As one of the most important nutrient elements in plants,nitrogen plays an important role in plant growth and development.Rice is an important food crop that feeds more than half of the world’s population.While a large amount of nitrogen fertilizer application greatly increased the yield of rice,it also caused nitrogen loss,low nitrogen-use efficiency,which have a serious impact on the ecological environment.Balancing rice yield and nitrogen-use efficiency has been a critical challenge in crop breeding.Hairy Leaf 6（HL6）is an AP2 class transcription factor that regulates leaf hair growth in rice.In the present study,the response of HL6 to nitrogen were analyzed by using a transcriptomic approach and phonotype analysis.The main results are as follows:1.The investigation of agronomic traits of HL6 transgenic lines showed that plant height of HL6 overexpression lines HL6-OX1was significantly lower than that of wild-type（WT）at the maturity stage.Investigation on yield related traits showed that overexpression of HL6 significantly decreased the effective panicle number per plant,panicle weight,primary branch number,filled grains number,seed setting ratio,yield per plant and 1000-grain weight.These results indicate that HL6 could affect agronomic traits such as plant type and inhibit the formation of rice yield.2.HL6 may negatively regulate crown root number:HL6 transgenic lines were cultivated in（NH4）2SO4and KNO3 nitrogen sources.Root phenotype analysis at seedling stage showed that the root length,root fresh weight and crown root number of overexpression lines HL6-OX1 were significantly reduced compared with WT.Compared with the control HL6-WT,the mutant HL6-MT showed no significant change in root length and root weight,and the number of crown roots increased significantly.3.Grain brown rice protein content of seeds of overexpression HL6 lines was significantly higher than that of WT.The protein content of brown rice grain in HL6insert mutant was significantly lower than that of the control HL6-WT.These results indicated that HL6 positively influences grain brown rice protein content.4.Gene expression analysis revealed that the expression of HL6 was induced by both ammonium and nitrate treatment,but the induction was lasted longer under ammonium treatment:HL6 expression was significantly up-regulated at 3 h after treatment with ammonium and nitrate,and the induced level reached the peak at 12 h,which was 3.4 and 2.7 times of the untreated level,respectively.At 48h after treatment,HL6 was induced by ammonium nearly 3 times,while the induced effect of nitrate treatment disappeared.5.Transcriptome analysis of the leaves and roots of HL6 seedlings exhibited that differentially expressed genes were enriched in the nitrogen metabolism pathway,diterpenoid biosynthesis pathway,and linoleic acid metabolism pathway.These results suggest that HL6 may be involved in regulating multiple biological processes.6.Real-time PCR analysis confirmed that overexpression of HL6 significantly inhibited the expressions of Os AMT1-2 and Os NRT2-2,suggesting that HL6 may negatively regulate genes related to the nitrogen metabolism pathway,thereby regulating plant growth and development.In this study,we reported that HL6,an AP2/ERF transcription factor,negatively regulated the expression of nitrogen metabolism genes Os AMT1-2 and Os NRT2-2,inhibited nitrogen uptake in roots,affected plant growth,and inhibited the formation of yield traits.HL6 responds to exogenous nitrogen induction and positively regulates protein content of grain brown rice.The results provided a new idea for exploring nitrogen uptake and utilization in rice roots. |
